Body dysmorphic disorder (BDD), a preoccupation with an imagined or slight defect in appearance, is a distressing, impairing, and under recognized disorder that is relatively common. It is a severe body image disorder that is associated with serious social and occupational impairment, high rates of hospitalization and suicide attempts, notably poor quality of life, and completed suicide. Although BDD is a significant public health problem, little research on its treatment has been done. While pharmacotherapy appears effective for BDD, a significant proportion of patients refuse, or are unresponsive to this treatment. Thus, it is critically important to develop effective psychological interventions. Recent studies suggest that cognitive behavioral therapy (CBT) is a promising treatment for BDD, but few CBT efficacy studies have been done, and a widely applicable CBT treatment manual is not available. This treatment development application proposes to develop, systemize, and pilot test a cognitive behavioral treatment for patients with BDD. The research team proposes to fully develop a treatment manual and accompanying therapist adherence and competence measures. Thereafter, CBT of 3 different durations will be openly applied by the treatment developers to BDD patients to determine which duration is clinically most useful and to revise the manual. In the study's final phase, the CBT treatment will be pilot tested using a waitlist control condition (n=36). Treatment effects on BDD symptoms, mood, functioning, quality of life, and other domains will be investigated, and possible predictors of treatment outcome will be explored. The resulting effect size will determine whether larger-scale randomized controlled trials of CBT for BDD are indicated. In summary, because there are no well-established psychosocial treatments for BDD, the proposed work will address an important gap in our knowledge and a pressing public health need, and it will lay essential groundwork for future, more definitive intervention studies for this common, severe, and understudied body image disorder.